Answer:
other phones = 173
iphones = 667
Explanation:
x = # of students with other phones
4x - 25 = # of students with iPhones
x + (4x - 25) = 840
5x - 25 = 840
5x = 840 + 25 = 865
x = 865/5 = 173
4(173) - 25 = 667
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